Tag: meteors

The annual Perseid meteor shower peaks over the next night or two, so this is the best time to go out and look. I have a guide on how to observe the shower and a couple of links, too, but first indulge me a moment to talk about meteor showers.

The Earth orbits the Sun, as do comets. Comets are lumpy collections of gravel and dust held together in a matrix of frozen ice (usually water and/or carbon dioxide). As they get near the Sun, the ice turns into a gas, freeing the dust and gravel. This material follows in the same path of the comet like dirt flying off a dump truck on a highway. Over time – millennia – it spreads out into space.

The Earth plows into this stuff as it goes around the Sun. These tiny bits of cosmic jetsam burn up as they ram into our atmosphere at speeds of up to 100 kilometers per second, and we call them meteors.

Quick tip: a meteoroid is the solid bit of rock or whatever that travels through space. As it burns up in our air we call it a meteor. If it hits the ground, it’s called a meteorite. Now you can sound pretentious and correct people at cocktail parties!

The Earth is always being bombarded by meteors; about 100 tons per day burn up in the atmosphere. But that number goes up when we pass through the stream of matter that’s come off a comet – think of it as driving down a road and hitting the occasional insect. Then you pass near a creek and suddenly you slam into a swarm of bugs.

So yeah, meteor showers are the equivalent of that. But much prettier and less disgusting.

Every August the Earth passes through the debris from the comet Swift-Tuttle, forming the Perseids meteor shower.

[The best place to observe the shower is apparently in Sarasota, Florida. Yes, this is a real picture; I took it myself.]

They’re called the Perseids because they appear to come from the sky in the constellation of Perseus. It’s a bit like when you drive through a tunnel and all the lights on the sides appear to be moving away from a point ahead of you. It’s perspective, an illusion of sorts. In this case, the orbits of the Earth and the meteoroids add together to make the meteors appear to shoot away from the part of the sky where Perseus is. Other showers do this too, but from different parts of the sky, and the showers are named after their constellation. Thus, the Leonids, the Orionids, the Taurids, and so on. The Perseids are one of the best of the year, with about 50 – 60 meteors per hour visible (so on average one per minute at the peak). You may see fewer than that, but sometimes there are mini-peaks where the number goes up. It’s worth going out for an hour or two to see them!

Tonight is one of the odder meteor showers of the years. Why is it odd? Well for one, it’s called the Quadrantids — named after a constellation that got redefined years ago and no longer exists. For another, the parent object of the shower isn’t a comet, it’s an asteroid that used to be a comet. And third, the shower peaks very sharply, coming and going in only an hour or two!

Here’s the deal.

First, meteor showers occur when the Earth plows through a trail of debris in space, usually left by a comet orbiting the Sun. The meteoroids — the solid bits of material — are usually very small, no bigger than a grain of sand. As they plow through our atmosphere at speeds of dozens of kilometers per second, they burn up, turning into meteors (if they hit the ground they’re called meteorites, which is very rare). Normally, you can see several random meteors every hour on a dark night, but during showers there may be dozens.

The length of time a shower lasts depends on how wide the debris field is. For most meteor showers it’s millions of kilometers wide, and so the showers can take days to play out. But the stream for the Quadrantids is very narrow, and the shower lasts for only an hour or so! It peaks tonight around 2 – 3 a.m. Eastern US time (07:00 – 07:00 GMT). That’s not an exact period, so if you want to see them you should go out an hour or so before then. There may be as many as 100 meteors per hour during that time!

Unfortunately, the waxing gibbous Moon is up tonight, so it’ll wash out a lot of the shooting stars. People on the east coast of the US have the best shot, since the Moon will hopefully have set by the time the shower peaks. However, Central time zone folks have a good view too since the Moon will be low to the horizon. I’ll give it a try tonight, since it peaks at midnight my time (in Boulder) and that’s early enough even for me to stay up.

As I said, meteor showers come from debris shed by comets as they orbit the Sun. These bits of stuff more or less follow the same orbit as their parent comet, and we get showers when the Earth rams through this material. However, the Quadrantids come from an object called 2003 EH1, which looks more like an asteroid — comets usually have lots of ice, but this object doesn’t. However, it’s on a comet-like orbit, so it most likely used to be a comet long ago which lost all its ice, leaving just rocky material behind.

And finally, the name: meteor showers appear to radiate from one point in the sky, in much the same way all the lights in a tunnel seem to be coming from ahead of you as you drive through that tunnel. Showers are named after the constellation where the meteors appear to come from: the Perseids for Perseus, the Orionids for Orion, and so on. Constellations are arbitrary boundaries in the sky, like state or county lines. Quadrans Muralis was a constellation defined back in the 19th century, and still existed when the Quadrantids were named, but was divided up when the modern official lines were drawn in 1930. That part of the sky is near the tail of the Big Dipper; so the meteors will appear to radiate away from the north across the sky.

So again, what to do: find a dark, open site. Try to bring a chaise longue or something where you can lie back and see lots of sky. Looking straight up is best. You don’t need binoculars or a telescope or anything like that: just your eyes, and a sense of wonder. Meteor showers can be a lot of fun, so I hope you see some good ones tonight!

Image credit: Randy Halverson. That’s not a meteor from the Quadrantids, but it’s still pretty.

A few days ago, three astronomers from Mexico posted a paper online (PDF) claiming that an observation from 1883 indicates a small comet passed within a few thousand kilometers of the Earth’s surface, and perhaps as close as 500km! Had this hit us, we would’ve been hammered by thousands of explosions as powerful as the largest nuclear explosions ever detonated.

The thing is, I’m not buying it. While superficially the interpretation fits the observations, there are way too many problems with it.

Here’s the deal. During the days of August 12 – 13, 1883, a Mexican astronomer named Jose A. y Bonilla reported seeing hundreds of objects passing directly in front of the Sun. They were small, appeared fuzzy, and left behind a misty appearance. In total, Bonilla says he saw 447 such objects!

The authors of this new work claim that what Bonilla may have seen was the remnants of a small comet that had previously fragmented. We’ve seen comets do this, and in fact it’s somewhat common. In 2006, Hubble took the picture shown above of the comet 73P/Schwassmann-Wachmann 3, which had recently disintegrated. So that part isn’t too far-fetched. However, once you make that assumption, things get pretty dicey.

The authors use the observations by Bonilla to estimate the distance and size of the comet fragments. Bonilla observed these objects at an observatory in Zacatecas, Mexico, but they were not seen transiting the Sun by any other observatories anywhere else. This can be used to narrow down their location; it means they must have been close to Earth. Had they been far away then other observatories would have seen them moving across the Sun. It’s like a bird flying by just outside your window; someone looking out a different window wouldn’t have seen it, but a bird a few hundred meters away would be visible to both.

Doing some simple math, the authors calculate the comet fragments were no closer than about 500 km (300 miles) from the Earth’s surface, and no farther than about 65,000 km (40,000 miles).

This right there is enough for me to be extremely skeptical of this idea. When a comet breaks up, it spreads out. Even when intact, the material surrounding a comet can be tens or even hundreds of thousands of kilometers across! Claiming that a comet broke apart, yet managed to constrain its pieces to volume of space less than a few thousand kilometers across strains credulity.

The annual Geminids meteor shower peaks tonight, so if you’re willing to brave the cold weather (assuming it’s cold where you are) then tonight is your best chance! I wrote a guide to watching meteors showers a while back (it’s for a different shower, but the general advice still holds true) that should help, too. I’ve heard rumors that things will be pretty good tonight for people on the east coast of the U.S. after midnight. If the clouds dissipate tonight I may go for them myself… now that it’s finally warmed up to the better side of the freezing point of water around here.

And if you do observe, you can join people across the planet and record your observations on Twitter using the hashtag #MeteorWatch. Universe Today has details.

The annual Leonid meteor shower peaks this year on or around Tuesday night. It’s a slow-peaking shower, so even if you go out tonight, or later than Tuesday, you’ll probably see a few meteors streaking across the sky.